Excited-state distortions and electron delocalization in mixed-valence dimers: Vibronic analysis of the near-IR absorption and resonance Raman profiles of [Fe-2(OH)(3)(tmtacn)(2)](2+)
Excited-state distortions and electron delocalization in mixed-valence dimers: Vibronic analysis of the near-IR absorption and resonance Raman profiles of [Fe-2(OH)(3)(tmtacn)(2)](2+)
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DOI：
10.1021/ic960413u
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发表时间：
1996-07-17
影响因子：
4.6
通讯作者：
Solomon, EI
中科院分区：
文献类型：
--
作者：
Gamelin, DR;Bominaar, EL;Solomon, EI
利用变温电子吸收光谱和共振拉曼光谱研究了Ⅲ类混合价态二聚体[Fe-2（OH）（3）（tmtacn）（2）]（2+）中与电子离域有关的近红外跃迁.激光激发到该吸收带导致在316和124 cm（-1）处完全对称的[Fe-2（OH）（3）]（2+）芯振动模式的主共振拉曼增强，其描述由简正坐标分析计算。振动分析的近红外共振拉曼激发配置文件和VT-吸收带形使用非谐激发态模型提供了一个描述的几何失真伴随着这种激励。[Fe-2（OH）（3）]（2+）核沿着Fe.. Fe轴，反映了该转变的显著的Fe-Fe σ-> σ * 特征。两种金属之间的基态σ相互作用已被确定为价离域的轨道路径，和σ-> σ * 失真分析被用来量化的电子耦合矩阵元素，H-AB，与此相关的结构依赖性路径。本文还讨论了全对称核坐标在[Fe-2（OH）（3）（tmtacn）（2）]（2+）的吸收光谱和RR光谱中的主导作用，以及与其它II类和III类混合价二聚体的Q（-）振动坐标和电子振动光谱的关系。结果表明，与完全对称坐标系下的有效激发态位移机制相比，Q（-）坐标系下的Q（-）坐标对[Fe-2（OH）（3）（tmtacn）（2）]（2+）的吸收光谱和RR光谱的贡献较小，这是由于Q（-）坐标系下的曲率变化机制效率较低。这与在II类混合价络合物的价间转移（TT）吸收和RR光谱中观察到的Q（-）坐标相对于其他全对称坐标的优势相反。
The near-IR transition associated with valence delocalization in the class III mixed-valence dimer [Fe-2(OH)(3)(tmtacn)(2)](2+) is studied using variable-temperature (VT) electronic absorption and resonance Raman (RR) spectroscopies to gain insight into the properties of electron delocalization in this dimer. Laser excitation into this absorption band leads to dominant resonance Raman enhancement of totally-symmetric [Fe-2(OH)(3)](2+) core vibrational modes at 316 and 124 cm(-1), descriptions of which are calculated from a normal coordinate analysis. Vibronic analysis of the near-IR resonance Raman excitation profiles and VT-absorption bandshapes using an anharmonic excited-state model provides a description of the geometric distortions accompanying this excitation. The excited-state distortion is dominated by expansion of the [Fe-2(OH)(3)](2+) core along the Fe ... Fe axis, reflecting the significant Fe-Fe sigma --> sigma* character of this transition. The ground-state sigma-interaction between the two metals has been identified as the orbital pathway for valence delocalization, and the sigma --> sigma* distortion analysis is used to quantify the structural dependence of the electronic-coupling matrix element, H-AB, associated with this pathway. The dominant role of totally-symmetric nuclear coordinates in the absorption and RR spectroscopies of [Fe-2(OH)(3)(tmtacn)(2)](2+) is also discussed in relation to the Q(-) vibrational coordinate and the vibronic spectroscopies of other class II and class III mixed-valence dimers. It is shown that intensity contributions from the Q(-) coordinate to the absorption and RR spectra of [Fe-2(OH)(3)(tmtacn)(2)](2+) are small relative to those of the totally-symmetric coordinates due to the inefficient change-in-curvature mechanism by which the Q(-) coordinate gains intensity, compared to the efficient excited-state displacement mechanism allowed for totally-symmetric coordinates. This is in contrast with the dominance of the Q(-) coordinate over other totally-symmetric coordinates observed in intervalence transfer (TT) absorption and RR spectroscopies of class II mixed-valence complexes.